A power-on reset circuit is used in order to secure the stable operation after starting to supply a power supply voltage in. various electronic devices. That is, the value of a power supply voltage supplied to an electronic device gradually increases from a ground potential level at the start of supply and will soon reach a constant level. If such a gradually-increasing power supply voltage value is directly provided to each circuit in an electronic device, the electronic device may not normally operate. Then, the power-on reset circuit, in the course of increasing of the power supply voltage value, provides a reset level voltage value to each circuit in the electronic device when the power supply voltage value is less than a threshold value, and will provide a power-supply voltage level voltage value to each circuit in the electronic device when the power supply voltage value becomes the threshold value or higher, thereby securing the stable operation of the electronic device.
Such a power-on reset circuit generally includes a bandgap reference circuit, a voltage dividing circuit, and a voltage comparison circuit as disclosed in Patent Documents 1 and 2. Even if there is a variation in the value of a power supply voltage to be supplied or a temperature variation, the bandgap reference circuit can output a voltage value with a small variation (hereinafter, referred to as a “first voltage value”).
On the other hand, the voltage dividing circuit includes a first resistor and a second resistor connected in series between a power supply voltage terminal to which the power supply voltage is supplied and a ground terminal, and outputs a voltage value, which is derived by dividing a power supply voltage value according to a ratio of the respective resistance values of the first resistor and second resistor, from a connection point between the first resistor and the second resistor. That is, the voltage dividing circuit outputs a voltage value (hereinafter, referred to as a “second voltage value”) proportional to the power supply voltage value.
Then, the voltage comparison circuit receives the first voltage value output from the bandgap reference circuit and the second voltage value output from the voltage dividing circuit, and outputs the reset level voltage value when the second voltage value is smaller than the first voltage value, and outputs the power-supply voltage level voltage value if the second voltage value becomes the first voltage value or higher.